Electrical Test Equipment Copyright © Texas Education Agency, 2011. All rights reserved.

Electrical Test Equipment

Copyright © Texas Education Agency, 2011. All rights reserved.

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LEARNING OBJECTIVES

Voltmeter use How to measure voltage Ammeter use How to measure current Ohmmeter use How to measure resistance Use of Ohm's Law


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Voltage Testing DevicesVoltage testers are used to measure or check the presents of voltage in an electrical circuit

Wiggy VoltmeterNeon Light


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Types of Voltage Testers

VT201, Non-Contact Voltage Detector Quickly check for the presence of ac

voltages, with no electrical contact Safe non-contact detection of voltages from

70 V to 440 V ac Both visible and audible indicators Detector emits loud audible chirping that

changes pitch based on probes proximity to the ac voltage source

Bright flashing LED also indicates presence of ac voltage

VT102, Voltage Tester 4 Bright neon lights indicate ac voltage 4 Ranges indicated from 110 V to 460 V ac No battery needed Tests 2 wire and 3 wire ac outlets


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Types of Voltage Testers

ST102, GFCI Socket Tester and

the ST101, Socket TesterTest GFCI breakers for proper wiring and operation

Easy to read light indicators show common wiring

problems

Confirm GFCI socket is wired for protection

GFCI circuit trips to confirm tester is working

Fast, easy socket test for use on 110-125 V ac

Confirm proper wiring and operation of ac socket

Wiggy® Solenoid Voltage Tester120V to 600V AC (50/60 Hz), or 120V to 600V DC

current.

Locates blown fuses, grounds and system leaks

quickly.

Has large, easy-to-read voltage indicator scale and

DC polarity indicator.

Operates without the use of batteries.


http://www.mytoolstore.com/klein/kln04.html

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Using a Voltage Tester

The simplest and least expensive tester is the

neon 2-wire 0-500 volt tester. Put one of the

leads on a ground reference (box screws, neutral

side of a plug, neutral or white wire, etc.) and the

other lead on the hot wire (hot side of a plug, black

or red wire, etc.) (see figures #1 and #2).

Figure 1: Neon 2-Wire 0-500 Volt Tester

Figure 2.

If the neon light glows, then you have voltage at the outlet, as is the case here.


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Using a Voltage Tester

Another handy device to have around is the "plug

tester". Just plug this device into a receptacle,

and it will not only tell you if there is voltage present,

but also if it is wired correctly. Just follow the codes

on the tester to determine the situation.

Figure 3: Plug Tester

Figure 4.


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Using a Voltage TesterThe type of meter that most electricians will use

is the digital multi-meter. These come in various

brand names, price ranges and quality, and the

old adage, "you get what you pay for" is the best

advice to follow here.

Figure 5: Digital Multi-Meter (Testing

from hot wire to box ground)

Figure 6: (Testing from neutral to box

ground. Notice the accuracy of only .077

volts AC)

*Note: The multi-meter will be discuss in detail later on in the presentation


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The Ammeter

It is essential that electricians be able to use

clamp-on ammeters, or multi-meters, for in-place

troubleshooting of motors and controllers as well

as other circuits. Many clamp-on ammeters can

be used to measure voltage and resistance as

well as current. They come in various sizes with

selections of scales that make them extremelyversatile tools.


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Using the AmmeterThe amps flowing through the cable registers on theLCD display. Because an amp clamp does not plugin to the line, there is no current loss and the readingis more accurate.

Clamp-on transformer jaws. Take current readingswithout interrupting service. Clamp around conductorsup to 1" (2-54cm) in diameter or 500MCM. 2" (5.08cm)Or 2000MCM for 1000 ampere models.

It allows current draw to be measured quickly andaccurately. The jaws of the clamp are clamped aroundone of the cables and the motor is started.


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Using the Ammeter

An amp clamp is a non-invasive method ofchecking current draw with any electrical set up.The jaws of the clamp are spring loaded so thatthey can be clamped around a cable; usuallythe positive lead in a DC electrical set-up. Itworks by measuring the impedance of thecurrent flowing through the cable.

This method has many benefits. It is easy to setup; you only have to be able to access one cableto be able to take a reading. It is non-invasivebecause you do not have to plug anything in tothe line between battery and speed controller, orbetween controller and motor. Plug in methodsare cumbersome (shunted meters or wattmeters),especially in the field, and always have someassociated power losses which make the reading

alittle inaccurate.

A sample test-bed for a brushless motor.Note that the amp-clamp jaws are clamped aroundthe positive lead between the battery pack andspeed controller. This is and older type of amp clampthat requires a separate multi-meter to take a reading;modern types have an LCD read-out built in to the unit


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Testing Electrical Circuits with the Multi-meter

A multimeter is an electrical instrument capable of measuringvoltage, current, and resistance. Digital multimeters havenumerical displays, like digital clocks, for indicating the quantityof voltage, current, or resistance. Analog multimeters indicatethese quantities by means of a moving pointer over a printedscale.

Analog multimeters tend to be less expensive than digitalmultimeters, and more beneficial as learning tools for the firsttime student of electricity. Connect the black lead to the common (-) hole. This may wellalready be done, depending on the type of meter you use.

Connect the red lead to the volts (+) hole. Be careful, if this leadIs placed in the wrong hole (ohm or amp) it can causepermanent damage to the meter. This may well already bedone, depending on the type of meter you use.

Turn the selector switch to AC volts (usually red). If there areMultiple selections, use the highest setting possible (if powerunknown) or go one level higher than the estimated power.Some digital meters have "Auto-range" and don't require anyselection apart from AC volts.


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Measuring Current in a CircuitCurrent is the measure of the rate of electron "flow" in acircuit. It is measured in the unit of the Ampere, simplycalled "Amp," (A).

The most common way to measure current in a circuit is to breakthe circuit open and insert an "ammeter" in series (in-line) with thecircuit so that all electrons flowing through the circuit also have togo through the meter. Because measuring current in this mannerrequires the meter be made part of the circuit, it is a more difficulttype of measurement to make than either voltage or resistance.

Some digital meters, like the unit shown in the illustration, have aseparate jack to insert the red test lead plug when measuringcurrent. Other meters, like most inexpensive analog meters, usethe same jacks for measuring voltage, resistance, and current.Consult your owner's manual on the particular model of meter youown for details on measuring current.

When an ammeter is placed in series with a circuit, it ideally dropsno voltage as current goes through it. In other words, it acts verymuch like a piece of wire, with very little resistance from one testprobe to the other. Consequently, an ammeter will act as a shortcircuit if placed in parallel (across the terminals of) a substantialsource of voltage. If this is done, a surge in current will result,potentially damaging the meter:


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Measuring Resistance in a CircuitResistance is the measure of electrical "friction" as electrons movethrough a conductor. It is measured in the unit of the "Ohm," that unitsymbolized by the capital Greek letter omega (Ω).

Set your multimeter to the highest resistance range available. The resistance function is usually denoted by the unit symbol for resistance: the Greek letter omega (Ω), or sometimes by the word "ohms."

Touch the two test probes of your meter together. When you do, the meter should register 0 ohms of resistance. If you are using an analog meter, you will notice the needle deflect full-scale when the probes are touched together, and return to its resting position when the probes are pulled apart.

The resistance scale on an analog multimeter is reverse-printed from the

other scales: zero resistance in indicated at the far right-hand side of the scale, and infinite resistance is indicated at the far left-hand side. There should also be a small adjustment knob or "wheel" on the analog multimeter to calibrate it for "zero" ohms of resistance. Touch the test probes together and move this adjustment until the needle exactly points to zero at the right-hand end of the scale.

Digital multimeters set to the "resistance" mode indicate non-continuity by displaying some non-numerical indication on the display. Some models say "OL" (Open-Loop), while others display dashed lines. If you are using a digital multimeter, you should see a numerical figure close to 10 shown on the display, with a small "k" symbol on the right-hand side denoting the metric prefix for "kilo" (thousand). Some digital meters are manually-ranged, and require appropriate range selection just as the analog meter. If yours is like this, experiment with different range switch positions and see which one gives you the best indication


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Measuring Resistance in a CircuitConnect the meter's test probes across the resistor as such, and note its

indication on the resistance scale: If the needle points very close to zero,

you need to select a lower resistance range on the meter, just as you

needed to select an appropriate voltage range when reading the voltage of a

battery.

Resistance is the measure of friction to electron flow through an object. The

less resistance there is between two points, the harder it is for electrons to

move (flow) between those two points. Given that electric shock is caused

by a large flow of electrons through a person's body, and increased body

resistance acts as a safeguard by making it more difficult for electrons to flow

through us, what can we ascertain about electrical safety from the resistance

readings obtained with wet fingers? Does water increase or decrease shock

hazard to people?

Be sure to never measure the resistance of any electrically "live“ object or

circuit. In other words, do not attempt to measure the resistance of a battery or

any other source of substantial voltage using a multimeter set to the resistance

("ohms") function. Failing to heed this warning will likely result in meter

damage and even personal injury.


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Using Ohm’s Law

Take and the measure the voltage and resistance ofa

circuit, use the Ohm's Law equation to calculate circuit

current. Compare this calculated figure with the

measured figure for circuit current:

Taking the measured figures for voltage and current, use

the Ohm's Law equation to calculate circuit resistance.

Compare this calculated figure with the measured figure

for circuit resistance:

Taking the measured figures for resistance and current, use the Ohm's Law equation to calculate circuit voltage. Compare this calculated figure with the measured figure for circuit voltage:


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Summary

Working with live electrical current can be very hazardous. Testing voltage output requires working with electrical current. Do not attempt this measurement without the proper tools and safeguards.

It is essential that electricians be able to use clamp-on ammeters, or multi-meters, for in-place troubleshooting of motors and controllers as well as other circuits.

Always test your test equipment for proper operation before use. A multimeter is an electrical instrument capable of measuring voltage, current,

and resistance. There are two types of multimeters, the digital and the analog meters.

Digital multimeters have numerical displays, like digital clocks, for indicating the quantity of voltage, current, or resistance. Analog multimeters indicate these quantities by means of a moving pointerover a printed scale.

Ammeters are use to check current in a circuit. An amp clamp is a non-invasive method of checking current draw with any electrical set up.


Electrical Test Equipment Copyright © Texas Education Agency, 2011. All rights reserved.

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Transcript of Electrical Test Equipment Copyright © Texas Education Agency, 2011. All rights reserved.